Process for producing core/sheath conjugate elastomer fiber

ABSTRACT

The present invention provides a process for producing a conjugate fiber that is excellent in strength, stretch elasticity, and transparency. The process includes a step (1) in which an elastomer resin (A) having stretching elasticity and an elastomer resin (B) having stretch elasticity, a permanent elongation of 25-70%, and a tensile elongation of 100-800% are separately melted and subjected to conjugate spinning using a conjugate spinneret having two nozzles so that the elastomer resin (A) forms a core and the elastomer resin (B) form a sheath; a step (2) in which the fiber obtained by composite spinning in the step (1) is heat-treated; and a step (3) in which the fiber heat-treated in the step (2) is stretched.

TECHNICAL FIELD

The present invention relates to a process of producing a material for stretch clothing such as stockings and panty stockings (PS).

BACKGROUND ART

Stretch fibers have been widely used as pantyhose fibers. Examples of stretch fibers commonly used are single covered yarn (SCY), in which one or several nylon fibers are wound around a polyurethane fiber, and double-covered yarn (DCY), in which one or several nylon fibers are wound in different directions, i.e., double-twisted, around a polyurethane fiber (see, for example, Patent Documents 1 and 2). Crimped conjugate fibers, which have a structure in which stretch fibers (e.g., polyurethane) and thermoplastic fibers (e.g., polyamide) are successively bonded in the lengthwise direction of the fibers, are also used (see, for example, Patent Documents 3 to 7). Many such fibers improved according to the elastic properties and strength of the desired clothing have been reported.

SCY and DCY, which have high supportability due to their excellent stretchability, have been widely used, but these yarns tend to have low transparency and increased thickness when woven into fabric. Furthermore, the production method thereof generally comprises stretching a polyurethane fiber to about two to about three times its original length, and coiling one or several nylon fibers around the polyurethane fiber about 2,000 to about 3,000 times per meter. Therefore, the production method is problematically time-consuming and expensive.

Conjugate fibers, which have a structure in which stretch fibers (e.g., polyurethane) and thermoplastic fibers (e.g., polyamide) are successively bonded in the lengthwise direction of the fibers, have advantageous features such as high transparency and low fabric thickness, compared to SCY and DCY. However, conjugate fibers generally have low supportability compared to SCY and DCY, because the conjugate fibers utilize supportability based on crimping, i.e., elasticity based on the stretching of the coiled fibers. It is thus difficult to fulfill the requirement of high supportability, which is in demand in the current market. Furthermore, the production method thereof comprises crimping the fibers by thermal contraction after being woven. Therefore, it is difficult to uniformly crimp the fibers, and the production method has problems such as poor quality control and low production yield.

-   Patent Document 1: Japanese Unexamined Patent Publication No.     S47-19146 -   Patent Document 2: Japanese Unexamined Patent Publication No.     S62-263339 -   Patent Document 3: Japanese Unexamined Patent Publication No.     S61-34220 -   Patent Document 4: Japanese Unexamined Patent Publication No.     S61-256719 -   Patent Document 5: Japanese Unexamined Patent Publication No.     H03-206122 -   Patent Document 6: Japanese Unexamined Patent Publication No.     H03-206124 -   Patent Document 7: Japanese Unexamined Patent Publication No.     2003-171831

DISCLOSURE OF THE INVENTION Problem to be Solved by the Invention

An object of the present invention is to provide a process of producing a conjugate fiber having excellent strength, stretch elasticity, and transparency.

Means for Solving the Problem

The present inventors conducted extensive research to achieve the above object, and found that when a sheath-core conjugate fiber composed of two different kinds of stretch fiber materials is formed by conjugate spinning and the fiber is heat-treated and then stretched, the obtained conjugate fiber has excellent crimpability and stretchability, while maintaining the transparency. The present invention was accomplished as a result of further research based on this finding.

The present invention provides the following methods of producing conjugate fibers.

Item 1. A process of producing a conjugate fiber comprising: (1) separately melting an elastomer resin (A) having stretch elasticity, and an elastomer resin (B) having stretch elasticity, a permanent elongation of 25 to 70%, and a tensile elongation of 100 to 800%, and subjecting the molten resins to conjugate spinning using a conjugate spinneret having two nozzles to form a bicomponent fiber in which the elastomer resin (A) forms a core and the elastomer resin (B) forms a sheath; (2) heat-treating the fiber obtained by conjugate-spinning in step (1); and (3) stretching the fiber heat-treated in step (2).

Item 2. A process according to Item 1, wherein the heat treatment temperature in step (2) is 40 to 80° C.

Item 3. A process according to Item 1 or 2, wherein the fiber is stretched to 1.25 to 4 times its original length in step (3).

Item 4. A process according to Item 1, 2 or 3, wherein the fiber is stretched in step (3) while heated at a temperature not lower than the heat treatment temperature of step (2).

Item 5. A process according to any one of Items 1 to 4, wherein the elastomer resin (A) is a polyurethane elastomer.

Item 6. A process according to any one of Items 1 to 5, wherein the elastomer resin (B) is a polyester-based elastomer and/or a polyamide-based elastomer.

Item 7. A process according to any one of Items 1 to 6, wherein the elastomer resin (B) contains inorganic fine particles.

Item 8. A process according to any one of Items 1 to 7, wherein the core and the sheath of the conjugate fiber have an eccentric circle or concentric circle configuration.

Item 9. A conjugate fiber produced by the process of any one of Items 1 to 8.

Item 10. A stretch clothing comprising the conjugate fiber of Item 9.

Item 11. A conjugate fiber comprising an elastomer resin (A) having stretch elasticity, and an elastomer resin (B) having stretch elasticity, a permanent elongation of 25 to 70%, and a tensile elongation of 100 to 800%; the conjugate fiber being a sheath-core fiber in which the core comprises the elastomer resin (A), and the sheath comprises the elastomer resin (B), and the area ratio of the core to the sheath in the cross-section of the fiber is in the range of 95:5 to 40:60.

The present invention will be described in detail below.

I. Conjugate Fiber

The conjugate fiber of the invention is an elastomeric sheath-core conjugate fiber comprising an elastomer resin (A) having stretch elasticity, and an elastomer resin (B) having stretch elasticity, a permanent elongation of 25 to 70% and a tensile elongation of 100 to 800%, wherein the core comprises the elastomer resin (A), and the sheath comprises the elastomer resin (B). A feature of the conjugate fiber of the present invention is that the core comprises an elastomer resin, and the sheath also comprises a specific elastomer resin (B).

When such conjugate fibers have an eccentric circle cross-section, the fibers are more easily crimped than those having a concentric circle cross-section by heat-treatment and stretching, and thus have high elasticity and enhanced supportability.

The conjugate fiber of the invention is produced by subjecting an elastomer resin (A) and an elastomer resin (B) to conjugate spinning to form a bicomponent fiber in which the elastomer resin (A) forms a core and the elastomer resin (B) forms a sheath; then heat-treating the conjugate fiber to promote cross-linking; and subsequently stretching the fiber. Therefore, the conjugate fiber of the invention is excellent in terms of transparency, stretch elasticity, strength, and elongation.

The elastomer resin (A), which forms the core of the conjugate fiber of the invention and has stretch elasticity, may be any thermoplastic elastomer that can return to approximately its original length after being stretched (i.e., has no yield point within the stretchable range), and more specifically has rubber elasticity (the capability of recovering to the length corresponding to the range of 10% on the hysteresis curve). Examples of elastomer resins (A) include polyurethane, polystyrene butadiene-based block copolymers, and the like. Polyurethane is particularly preferable.

The elastomer resin (A) preferably has a high tensile strength (JIS K7311) of about 30 to about 60 MPa, and more preferably about 45 to about 60 MPa. The tensile elongation (JIS K7311) of the elastomer resin (A) is preferably about 400 to about 900%, and more preferably 400 to 600%. The surface hardness A (JIS K 6253) of the elastomer resin (A) is preferably about A70 to 98, and more preferably about A80 to 90. When the surface hardness A is less than A70, it is difficult to secure the strength. When the surface hardness A is more than A98, the elongation and stretchability tend to severely deteriorate.

Examples of elastomer resin (A) include Kuramilon U-3195, 8175, etc. (products of Kuraray Co., Ltd.), Pandex T-1185N, 1190N, 1195N, etc. (products of DIC Bayer Polymer Ltd.), and the like.

As an example of the production process of the elastomer resin (A), a polyurethane elastomer resin production process is described below. The polyurethane elastomer resin can be produced, for example, from an aromatic polyisocyanate and a polyol, using a known method such as the one-shot method, the prepolymer method, or the like.

Examples of aromatic polyisocyantates used as a raw material include aromatic diisocyanates having 6 to 20 carbon atoms (except for the carbons in the NCO groups; the same is applied hereinafter), modified products of such aromatic diisocyanates (modified diisocyanates having a carbodiimide group, a urethodione group, a urethoimine group, a urea group, etc.), and a mixture of two or more thereof.

Specific examples of aromatic polyisocyantates include 1,3- and/or 1,4-phenylenediisocyanate; 2,4- and/or 2,6-tolylene diisocyanate; 2,4′- and/or 4,4′-diphenylmethanediisocyanate (hereinafter abbreviated as MDI); 4,4′-diisocyanatobiphenyl; 3,3′-dimethyl-4,4′-diisocyanatodiphenylmethane; 1,5-naphthylene diisocyanate; and the like. Among these, MDI is particularly preferable.

Examples of polyols used as a raw material include polyether-based polyols, polyester-based polyols, polycarbonate-based polyols, aliphatic-based polyols, and the like. Polyether-based polyols and polyester-based polyols are particularly preferable.

The number average molecular weight of the polyol is preferably 300 or more, more preferably 1,000 or more, and most preferably 2,000 or more in terms of the softness of the obtained fiber. The number average molecular weight of the polyol is preferably 4,000 or less, more preferably 3,500 or less, and most preferably 3,000 or less, in terms of fiber elasticity.

The elastomer resin (B), which forms the sheath of the conjugate fiber of the invention, is a thermoplastic elastomer resin having stretch elasticity and a permanent elongation of 25 to 70%. The permanent elongation is defined in accordance with JIS K 6251. More specifically, when stretched 100% or more, the resin (B), even with stretch elasticity, is not restored to its original shape, but to a stretched, stabilized state.

This is because in the original state of the elastomer resin (B), the hard segment and the soft segment that form the elastomer resin (B) are randomly oriented; however, when the elastomer resin (B) is stretched 100% or more, the hard segment is oriented in a certain direction and cannot be restored to the original state, and only the soft segment retains its stretch elasticity. The conjugate fiber of the present invention takes full advantage of this property of the elastomer resin (B) to exhibit high supportability.

The permanent elongation (JIS K 6251) of the elastomer resin (B) is about 25 to about 70%, preferably about 30 to about 70%, and more preferably about 40 to about 60% at 100% elongation. To determine the permanent elongation, a dumbbell-shaped specimen is stretched to a predetermined elongation of 100% (i.e., elongated to twice its original length) under tensile load, and then allowed to stand in that state for 10 minutes. Subsequently, the load is promptly released and the specimen is allowed to stand for 10 minutes. The ratio of the elongated length to the original length after being left for 10 minutes is calculated and defined as the permanent elongation (%). When the permanent elongation is less than 25%, the obtained conjugate fiber cannot have high supportability. When the permanent elongation exceeds 70%, significant plastic deformation occurs, and a property of the elastic body, i.e., stretchability, is reduced.

The elastomer resin (B) preferably has a high tensile strength (ASTM D638) of about 10 to about 40 MPa, and more preferably about 25 to about 40 MPa. The tensile elongation (ASTM D638) of the elastomer resin (B) is preferably about 100 to about 800%, and more preferably 400 to 600%. When the tensile elongation is less than 100%, the resin has insufficient stretchability, and thus cannot be used for this purpose. When the tensile elongation is more than 800%, the resin generally has low strength and cannot have high supportability. The surface hardness D (ASTM D2240) of the elastomer resin (B) is preferably about D30 to about D70, and more preferably D35 to D60. When the elastomer resin (B) has a surface hardness of less than D30, shape retention after being stretched is difficult because the surface is overly soft, and feeling to the touch also tends to be impaired. When the surface hardness is more than D70, high shape retention (settability) after being stretched is achieved, but the stretch elasticity tends to be deteriorated due to the low elastomeric property.

Specific examples of the elastomer resin (B) having the above-mentioned properties include urethane-based elastomers (TPU), polyester-based elastomers, polyamide-based elastomers, styrene-butadiene-based elastomers, and the like. These elastomer resins can be prepared by known methods. Commercially available resins can also be used.

Examples of urethane-based elastomers include block copolymers comprising a soft segment containing a polyol component, and a hard segment containing an organic polyisocyanate component. Specific examples thereof include polyester-based polyurethane elastomers, polycaprolactone-based polyurethane elastomers, polycarbonate-based polyurethane elastomers, polyether-based urethane elastomers, and the like. For example, Kuramilon manufactured by Kuraray Co., Ltd., and Pandex manufactured by DIC Bayer Polymer Ltd. can be used.

Examples of polyester-based elastomers include polyether (or polyester) ester block copolymers comprising a hard segment containing an aromatic polyester component, and a soft segment containing a polyether component or a polyester component. Examples of aromatic polyester components for hard segments include polybutylene terephthalate (PBT), and the like. Examples of polyether components or polyester components for soft segments include polytetramethylene glycol (PTMG), polycaprolactone (PCL), and the like. Any of these compounds can be used in the present invention. Polyether ester block copolymers are preferably used.

Specific examples of polyester-based elastomers include Pelprene (P-type, S-type, etc.) manufactured by Toyobo Co., Ltd., Hytrel manufactured by Du Pont Toray Co., Ltd., REXE manufactured by Teijin Co., Ltd., and the like. Polyester-based elastomers disclosed in Japanese Unexamined Patent Publications Nos. H11-302519 and 2000-143954 can also be used.

Examples of polyamide-based elastomers include block copolymers comprising a hard segment containing a polyamide component, and a soft segment containing either or both a polyether component and a polyester component. Specific examples thereof include Pebax manufactured by Arkema Co., Ltd., the PAE series manufactured by Ube Industries, Ltd., and the like.

Examples of styrene butadiene-based elastomers include block copolymers comprising a hard segment containing a polystyrene component, and a soft segment containing a polyolefin component. Specific examples thereof include styrene-ethylene-butylene-styrene block copolymer (SEBS), and the like.

In addition to an eccentric circle configuration and a concentric circle configuration, the sheath and core of the conjugate fiber of the invention may have a side-by-side configuration, because the conjugate fiber with a side-by-side configuration can be significantly crimped by thermal contraction. Among these, the eccentric circle configuration is preferable in terms of feeling to the touch.

The core comprising the elastomer resin (A) accounts for about 40 to about 95%, preferably about 50 to about 90% of the cross-sectional area of the fiber. In other words, the area ratio of the core comprising the elastomer resins (A) to the sheath comprising the elastomer resins (B) is in the range of about 95:5 to about 40:60, and preferably about 90:10 to about 50:50. When the area ratio is within the above-mentioned range, the obtained conjugate fiber can have high supportability. When the core accounts for less than 40% of the cross-sectional area, high supportability cannot be obtained due to a high area ratio of the elastomer resin (B) in the cross-section, whereas when the core accounts for more than 95%, the fiber is unlikely to return to the same shape and length after being stretched.

The diameter of the conjugate fiber of the invention is not particularly limited, but is usually about 20 to about 100 μm, and preferably about 30 to 80 μm. In particular, when the fiber is used as a material for panty stockings (PS), a diameter of about 40 to about 70 μm is preferable.

As described above, the elastomer resin (A), which forms the core and has stretch elasticity, has no yield point within the stretchable range, and more specifically cannot be stretched beyond the elastic limit, whereas the elastomer resin (B) has stretch elasticity and a yield point within its stretchable range. Therefore, the conjugate fiber of the invention inherits these properties of the elastomer resins. More specifically, when the conjugate fiber of the invention is stretched beyond the yield point of the elastomer resin (B), the elastomer resin (B) is recovered to the length at the yield point of the elastomer resin (B) and stabilized, whereas the elastomer resin (A) remains in a stretched state and retains its stretch elasticity at the yield point of the elastomer resin (B) Therefore, the conjugate fiber comprising these resins has remarkably improved supportability. This point is easily understood by referring to, for example, FIG. 1.

The conjugate fiber of the present invention has advantageous features such as high transparency and low thickness, when woven into fabric.

Therefore, the conjugate fiber of the invention can be suitably used for stockings, pantyhose, and the like that particularly require these functions. However, the use of the fiber is certainly not limited thereto, and can be used for other clothing.

II. Production Process of Conjugate Fiber

The conjugate fiber of the present invention can be prepared by a process including: step (1) in which an elastomer resin (A) having stretch elasticity, and an elastomer resin (B) having stretch elasticity, a permanent elongation of 25 to 70%, and a tensile elongation of 100 to 800% are separately melted and subjected to conjugate spinning using at least one conjugate spinneret having two nozzles to form a bicomponent fiber comprising the elastomer resin (A) as a core and the elastomer resin (B) as a sheath; step (2) in which the fiber obtained by conjugate spinning in step (1) is heat-treated; and step (3) in which the fiber heat-treated in step (2) is stretched.

In step (1), the specific elastomer resin (A) and elastomer resin (B) are separately melted at temperatures suitable for spinning and subjected to conjugate spinning to form a bicomponent fiber comprising the elastomer resin (A) as a core and the elastomer resin (B) as a sheath. As long as such bicomponent conjugate spinning can be carried out, any known spinning method and spinning apparatus can be used. The area ratio of the core to the sheath in the cross-section of the fiber can be appropriately adjusted by changing the amounts of resins extruded. The core/sheath area ratio is preferably in the range of about 95:5 to about 40:60, as described above.

To impart dye-affinity to the fiber, the elastomer resin (B) of the sheath may be blended and modified with a dyeable resin (for example, nylon, polyester, etc.). Examples of dyeable resins that can be used include polyamide-, polyester-, acryl-, and vinylon-based resins. Polyamide-based resins and polyester-based resins are preferably used. The amount of dyeable resin used is selected in accordance with the dye-affinity of the elastomer resin (B). The lower limit of the dyeable resin content is preferably 1 wt. %; and the upper limit thereof is preferably 30 wt. %, and more preferably 10 wt. %. When the dyeable resin content is less than 1 wt. %, color development by dyeing is low. When the dyeable resin content is over 30 wt. %, the strength and elongation of the fiber may be reduced. Furthermore, the spinnability is impaired.

Such a mixture can be prepared by mixing a dyeable resin as described above with the elastomer resin (B), and feeding the mixture into an extruder. To obtain stable physical properties, uniform dispersion of the dyeable resin is preferable. Therefore, the mixture is more preferably obtained by preparing a mixed raw material using a biaxial kneading machine and feeding the material into an extruder.

High-fashion pantyhose that is very soft to the touch and that can be dyed various colors can be thus prepared.

To improve softness to the touch, inorganic fine particles or the like may be dispersed on the surface of the elastomer resin (B) of the sheath in the conjugate fiber of the invention.

Inorganic fine particles that can be used are not particularly limited. Examples of such inorganic fine particles include light calcium carbonate, heavy calcium carbonate and like calcium carbonates; barium carbonate; basic magnesium carbonate and like magnesium carbonates; kaolin, talc, calcium sulfate, barium sulfate, titanium dioxide, titanium oxide, zinc oxide, magnesium oxide, ferrite powder, zinc sulfide, zinc carbonate, satin white, calcined diatomaceous earth, and like diatomaceous earth; calcium silicate, aluminum silicate, magnesium silicate, amorphous silica, non-crystalline synthetic silica, colloidal silica and like silica; colloidal alumina, pseudo-boehmite, aluminium hydroxide, magnesium hydroxide, alumina, lithopone, zeolite, aluminosilicate, activated clay, bentonite, sericite, and like mineral pigments. These compounds may be used singly or in a combination of two or more. Among these, titanium oxide, zinc oxide, barium sulfate, and silica are preferable.

The shape of the inorganic fine particles is not particularly limited. Regularly shaped particles, or irregularly shaped particles in the form of balls, needles, plates and the like can be used.

The average particle diameter of the inorganic fine particles is such that the lower limit is preferably 0.20 μm and the upper limit is preferably 3.00 μm. Inorganic fine particles with an average particle diameter of less than 0.20 μm may insufficiently reduce discomfort such as stickiness in humid conditions. When inorganic fine particles with an average particle diameter greater than 3.00 μm are used to produce clothing, the texture and feeling to the touch may be impaired and the strength of the fiber may be reduced.

The lower limit of the inorganic fine particle content is preferably 2 wt. %, and the upper limit thereof is preferably 30 wt. %, and more preferably 7 wt. %. An inorganic fine particle content of less than 2 wt. % may insufficiently reduce discomfort such as stickiness under humid conditions. An inorganic fine particle content of over 30 wt. % may reduce the strength and elongation of the fiber. Furthermore, the spinnability is also impaired.

Such a mixture can be prepared by mixing inorganic fine particles with the elastomer resin (B) and feeding the mixture into an extruder. To obtain stable physical properties, uniform dispersion of the inorganic fine particles is preferable. Therefore, the mixture is more preferably obtained by preparing a mixed raw material using a biaxial kneading machine and feeding the material into an extruder.

In step (2), the conjugate fiber obtained in step (1) is heat-treated, prior to the stretching of step (3). The heat treatment is performed to cross-link the urethane elastomer, thereby enhancing the recovery power (stretch-back ability). The heat treatment temperature is in the range of about 40° C. to about 80° C. When the heat treatment temperature is more than 80° C., the resin is deteriorated. When the heating temperature is less than 40° C., insufficient cross-linking results. Preferable conditions are a heat treatment temperature of 50 to 65° C.

In general, this heat treatment is preferably performed under wet heat conditions, although it may vary depending on the cross-linking process of the urethane elastomer. More specifically, the heat treatment is preferably performed at the above-mentioned temperature at a relative humidity of 20 to 80% RH, and more preferably 30 to 70% RH.

In step (3), the heat-treated fiber is stretched to about 1.25 to about 4 times, and preferably 2 to 4 times, its original length. Considering the balance between the strength and the elongation, the stretch magnification is set within the above range. When the stretch magnification is too low, the strength is insufficient. When the stretch magnification is too high, the elongation is impaired. From these viewpoints, the stretch magnification is preferably 2.5 to 3.5 times, and most preferably 2.9 to 3.1 times the original length.

To inhibit fiber whitening and sufficiently crimp the fiber, stretching the fiber while heated is preferable. In particular, stretching the fiber while heated at a temperature not lower than the heat treatment temperature of step (2) (for example, about 40° C. to about 80° C.) is preferable.

The conjugate fiber produced by the above process can have a tensile strength in the range of about 1.0 to about 4.0 cN/dtex, and preferably 1.0 to 3.5 cN/dtex, and a tensile elongation in the range of about 50 to about 300%, and preferably 100 to 250%. The tensile strength and tensile elongation are values obtained according to JIS L1095 using a Shimadzu Autograph AGS-J with an initial load of zero and a width between chucks of 5 cm at a stretching rate of 300 mm/min. The tensile strength and tensile elongation can be adjusted to the desired ranges by selecting the kinds of elastomer resins (A) and (B), the sheath/core ratio, the stretch magnification, etc.

The conjugate fiber of the present invention thus produced has excellent strength, stretch elasticity, and transparency, and thus has beautiful appearance and excellent supportability. Therefore, the conjugate fiber of the invention is particularly suitable for use as a material for stockings and pantyhose, and can also be suitably used for other objects that require similar functions.

Effects of the Invention

The conjugate fiber of the present invention is advantageously thinner than known covered yarns such as SCY and DCY, and also has high transparency. Furthermore, the conjugate fiber of the invention can be produced very easily at low cost, thus achieving high productivity.

The conjugate fiber of the invention has advantageously high strength and elasticity, and excellent supportability, compared to conjugated yarns composed of known stretch fibers and thermoplastic fibers.

The conjugate fiber of the invention is an excellent stretchable clothing material that eliminates the defects of known covered yarn and conjugated yarn, and has the advantages of both types of yarns.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view showing the stretching behavior of the conjugate fiber of the invention. The elastomer resin (A) (e.g., polyurethane) returns approximately to its original length after being stretched. In other words, the elastomer resin (A) is stretched within the range not reaching its yield point. The elastomer resin (B) (e.g., polyester elastomer) is stretched beyond its yield point and recovered to the length at the yield point thereof after being stretched. The conjugate fiber of the invention is stretched beyond the yield point of the elastomer resin (B) of the sheath, and recovered to the length at the yield point of the elastomer resin (B) after being stretched. The elastomer resin (A) of the core retains its stretch elasticity at the yield point of the elastomer resin (B).

FIGS. 2( a) and 2(b) show the data on tensile strength and tensile elongation of the conjugate fibers obtained by stretching the fibers to one to four times its original length in Example 1.

FIG. 3( a) is a cross-sectional photograph of the conjugate fiber obtained in Example 2; and FIG. 3( b) is a photograph (b) of the crimped state of the conjugate fiber.

FIG. 4 is a photograph of the conjugate fiber obtained in Comparative Example 3.

FIG. 5 is a schematic diagram of the measuring apparatus used to evaluate the light transmittance (transparency) of the pantyhose fabric.

BEST MODE FOR CARRYING OUT THE INVENTION

The invention will be described in more detail below by way of Examples and Comparative Examples, which are not intended to limit the invention.

Example 1

A thermoplastic polyurethane (Pandex T-1190N; product of DIC Bayer Polymer Ltd., surface hardness A (JIS K 6253): 90), and a polyester-based elastomer (Pelprene P-150B; product of Toyobo Co., Ltd.; tensile strength and elongation (ASTM D638): 38 MPa and 500%, permanent elongation (JIS K6251): 59%, surface hardness D (ASTM D2240): 57) were separately melted by heating at barrel temperatures of 180 to 205° C. and 190 to 220° C., respectively, using single screw extruders, and the amounts of molten products were measured with gear pumps. The molten products were then conjugate-spun with a conjugate spinneret having two nozzles heated at 225° C. to form a concentric bicomponent fiber composed of the thermoplastic polyurethane as a core and the polyester-based elastomer as a sheath. The area ratio of the thermoplastic polyurethane to the polyester-based elastomer in the cross-section of the bicomponent fiber was controlled by adjusting the ratio of the components extruded by the gear pumps.

More specifically, the bicomponent fiber was wound in an unstretched state at a winding rate of 200 m/min with a silicon oil applied to the surface thereof. After the obtained bicomponent fiber is heat-treated (in a wet heat environment, at 55% RH and 60° C.) in a subsequent step, the fiber is stretched to one, two, three, or four times its original length while heated at 60° C. FIG. 2 shows the tensile strength and tensile elongation of the obtained fiber. The tensile strength and tensile elongation were measured according to JIS L1095 using a Shimadzu Autograph AGS-J with an initial load of zero and a width between chucks of 5 cm at a stretching rate of 300 mm/min. The fiber obtained after being stretched to three times its original length had a diameter of 59 μm, and the core accounted for 51% of the cross-sectional area of the fiber.

FIG. 2 (a) shows that the tensile strength increases in proportion to the draw magnification. FIG. 2 (b) shows that the tensile elongation decreases in inverse proportion to the draw magnification. In general, as shown in FIG. 2, tensile strength multiplied by tensile elongation is often constant in the same fiber.

Example 2

A conjugate fiber was produced in a similar manner as in Example 1. More specifically, the area ratio of the thermoplastic polyurethane to the polyester-based elastomer in the cross-section of the bicomponent fiber was changed by adjusting the amounts of components extruded by the gear pumps, and the fiber was stretched to three times its original length while heated at 60° C. The core of the obtained fiber accounted for 78% of the cross-sectional area of the fiber, and the diameter of the fiber was 63 μm. FIGS. 3( a) and 3(b) show the cross-section and crimped state of this fiber.

FIG. 3( a) shows that the core is surrounded by a thin sheath having a concentric circle configuration. FIG. 3( b) shows that the fiber is crimped and transparent.

Comparative Example 1

A conjugate fiber was produced in a similar manner as in Example 1, except that a polyamide (nylon-6) was used in place of the polyester-based elastomer in Example 1. The fiber was stretched to three times its original strength. The diameter of the obtained fiber was 60 μm, and the core accounted for 56% of the cross-sectional area of the fiber.

Comparative Example 2

A single covered yarn composed of a polyurethane elastic yarn measuring 22 dtex as a core yarn, and a nylon yearn measuring 11 dtex/5 filaments as a covering yarn twisted around the polyurethane elastic yarn in the S-direction was produced.

Comparative Example 3

A conjugate fiber was produced in a similar manner as in Example 1, except that the heat treatment step (in a wet heat environment, at 55% RH and 60° C.) was not performed and the fiber was stretched to three times its original strength while heated at 25° C. The core of the obtained fiber accounted for 78% of the cross-sectional area of the fiber, and the diameter of the fiber was 63 μm. FIG. 4 shows this fiber.

FIG. 4 shows that the fiber has a white surface and is not crimped. This fiber is clearly different from the crimped, transparent fiber of Example 2, shown in FIG. 3( b).

Example 3

Using a single cylinder knitting machine, a cylindrical fabric was woven in a plain weave (plain stitch) from the conjugate fiber obtained by stretching the bicomponent fiber to three times its original length in Example 1. After the toe ends and panty part of the pantyhose were seamed in accordance with a standard method, the pantyhose fabric was dyed (beige; carlo), and heat-set on a foot mold to produce pantyhose.

Example 4

Pantyhose were produced in a similar manner as in Example 3, using the conjugate fiber of Example 2.

Comparative Example 4

Pantyhose were produced in a similar manner as in Example 3, using the conjugate fiber of Comparative Example 1.

Comparative Example 5

Pantyhose were produced in a similar manner as in Example 3, using the single covered yarn of Comparative Example 2.

Comparative Example 6

Pantyhose were produced in a similar manner as in Example 3, using the conjugate fiber of Comparative Example 3.

Test Example 1

The pantyhose obtained in Examples 3 and 4 and Comparative Examples 4 to 6 were subjected to the following evaluation tests.

Evaluation of Stretch Elasticity:

The stretch elasticity of the pantyhose fabric was evaluated based on the tensile strength (lateral stretch). A stretching tool was attached to an ankle portion of the pantyhose, and the tensile strength (unit: cN) was measured with a width between chucks of 5 cm and an initial chuck-to-chuck distance of 15 cm at a stretching rate of 300 mm/min. Using a Shimadzu Autograph AGS-J, the tensile strength was measured at a 30 cm elongation, a maximum elongation of 40 cm, and a recovery to 30 cm elongation.

Evaluation of Transparency:

A black cylinder (diameter: 115 mm, FIG. 5) with 40 mm-diameter holes formed on the lateral surface was covered with one sheet of pantyhose fabric. Light was emitted from a light source provided in the cylinder, and the quantity of light transmitted through the pantyhose fabric (unit: LUX) was measured.

The light transmittance was calculated by the following equation:

(The amount of light transmitted through the fabric/The amount of light measured without using the fabric (blank, 200 LUX))×100.

The transparency was thereby evaluated.

TABLE 1 Measurement parameters Stretch elasticity: measured at the ankle portion At a At a At a maximum recovery Transparency 30 cm elongation to 30 cm (Light elongation of 40 cm elongation transmittance) Example 3 686.9 1485.5 125.1 91.9 Example 4 1625.7 2433.3 409.4 93.3 Comparative 441.5 1353.8 116.4 92.9 Example 4 Comparative 1144.3 2153.4 425.5 84.5 Example 5 Comparative 590 1608 101 88.8 Example 6

Table 1 shows that compared to the pantyhose of Comparative Examples 4 and 5, the pantyhose of Examples 3 and 4 have high transparency and a high recovery after being stretched to a certain fixed length.

Compared with the pantyhose of Comparative Example 6, the pantyhose of Example 4 have remarkably excellent transparency and a remarkably excellent recovery after being stretched to a certain fixed length. The pantyhose of Example 4 was produced using the fiber of Example 2, whereas the pantyhose of Comparative Example 6 was produced using the fiber of Comparative Example 3. The results show that the remarkable performance differences therebetween are attributable to the characteristics of these fibers. 

1. A process of producing a conjugate fiber comprising: (1) separately melting an elastomer resin (A) having stretch elasticity, and an elastomer resin (B) having stretch elasticity, a permanent elongation of 25 to 70%, and a tensile elongation of 100 to 800%, and subjecting the molten resins to conjugate spinning using a conjugate spinneret having two nozzles to form a bicomponent fiber comprising the elastomer resin (A) as a core and the elastomer resin (B) as a sheath; (2) heat-treating the fiber obtained by conjugate spinning in step (1); and (3) stretching the fiber heat-treated in step (2).
 2. A process according to claim 1, wherein the heat treatment temperature in step (2) is 40 to 80° C.
 3. A process according to claim 1, wherein the fiber is stretched to 1.25 to 4 times its original length in step (3).
 4. A process according to claim 1, wherein the fiber is stretched in step (3) while heated at a temperature not lower than the heat treatment temperature of step (2).
 5. A process according to claim 1, wherein the elastomer resin (A) is a polyurethane elastomer.
 6. A process according to claim 1, wherein the elastomer resin (B) is a polyester-based elastomer and/or a polyamide-based elastomer.
 7. A process according to claim 1, wherein the elastomer resin (B) contains inorganic fine particles.
 8. A process according to claim 1, wherein the core and the sheath of the conjugate fiber have an eccentric circle or concentric circle configuration.
 9. A conjugate fiber produced by the process of any one of claims 1 to
 8. 10. A stretch clothing comprising the conjugate fiber of claim
 9. 11. A conjugate fiber comprising an elastomer resin (A) having stretch elasticity, and an elastomer resin (B) having stretch elasticity, a permanent elongation of 25 to 70%, and a tensile elongation of 100 to 800%; the conjugate fiber being a sheath-core fiber in which the core comprises the elastomer resin (A), and the sheath comprises the elastomer resin (B), and the area ratio of the core to the sheath in the cross-section of the fiber is in the range of 95:5 to 40:60. 